There has been a perennial need for improved heavy support weapons for military forces. The fifty caliber machine gun has for years been the basic heavy support weapon for American armed forces as well as the armed forces of various other countries. Certain forces employ 25, 30 and 40 millimeter weapons but such generally are too heavy to be man-carried and exhibit such recoil forces that special heavy mounts are needed. This limits their application to larger vehicles. Moreover, such weapons have shorter effective range than the existing 50 caliber machine gun. Therefore, the existing 40 millimeter heavy support weapons fall far short of meeting essential military requirements.
Other requirements not fully satisfied by existing weapons are the need for both automatic open bolt and semi-automatic closed bolt operation and for recoil operation, not externally powered or blowback operated. Minimum recoil for the projectile and load size are desired thereby minimizing the shock loading on the trunnion or other mount. The weapon must be reliable, easily maintained and, if possible, field strippable without special tools. The above requirements, while recognized, have not heretofore been achieved.
Over and above these requirements, the weapon must be accurate in first round firing in either semi-automatic or full automatic firing modes. Accuracy cannot be sacrificed to achieve any of the other above objectives.